This invention relates to the field of treating vitamin deficiency conditions and to preparations for use in such treatment.
Vitamin B12 is a cobalt-containing vitamin which is involved in a number of biochemical reactions. The two most important are the conversion of homocysteine to methionine and the conversion of methylmalonyl-coenzyme A to succinyl-coenzyme A. Homocysteine is potentially harmful to many body tissues, including the vascular system and the nervous system, if it is present in excess. Methionine is required for the formation of S-adenosyl-methionine which is used as a methyl donor in many different essential reactions including the regulation of DNA and RNA function and the synthesis of phospholipids, neurotransmitters and complex carbohydrates. The formation of succinyl-coenzyme A is required for the normal metabolism of fats and carbohydrates. It is thus apparent that an inadequate supply of vitamin B12 will lead to many different abnormalities in the body. The best known are the haematological abnormality of megaloblastic anaemia, and neurological damage which can lead to fatigue and to a range of neurological and psychiatric symptoms which are caused by loss of neuronal function proceeding to neurodegeneration.
Vitamin B12 has a particularly close interaction with folic acid. The conversion of homocysteine to methionine is achieved by the enzyme methionine synthetase where methyl-cobalamin plays an essential role. A required co-factor for this enzyme is folic acid in the form of 5-methyltetrahydrofolate: in the course of the reaction a methyl group is transferred from 5-methyltetrahydrofolate to homocysteine, so producing tetrahydrofolate and methionine. As a result of this reaction deficiencies of folic acid and of vitamin B12 interact. This interaction is important both in the lowering of homocysteine and in the generation of S-adenosyl-methionine for methylation reactions.
Methylation is increasingly being recognised as a reaction of central importance in many different reactions in all the tissues of the body, but particularly the brain, the liver and rapidly dividing tissues like the bone marrow, the gastrointestinal tract, the skin and the reproductive system. The methyl donor which plays the key role in over thirty reactions is S-adenosyl-methionine (SAM) (T Bottiglieri et al, Drugs 1994; 48; 137-152. P K Chiang et al, FASEB J 1996; 10; 471-480. T Bottiglieri, Exp Opin Invest Drugs 1997; 6; 417-426. C S Lieber, J Hepatology 1999; 30; 1155-9). Methylation of the nucleic acids, DNA and RNA, plays a central role in the regulation of gene function and expression. Methylation regulates the functions of many enzymes, including enzymes involved in the synthesis of the neurotransmitters noradrenaline, dopamine and serotonin. Methylation modulates the behaviour of many receptors, including those for noradrenaline, adrenaline, acetyl choline, gamma-amino-butyric acid and many other substances. Methylation is important in the synthesis of key membrane phospholipids and in the regulation of the properties of all the external and internal phospholipid-containing membranes of cells. Methylation is required for the normal synthesis of the polyamines, spermine and spermidine, which are important signalling molecules in many cells. Methylation is important in the synthesis of complex carbohydrates which modify many cell-cell interactions. Since vitamin B12 and folic acid are absolutely required for the normal synthesis of SAM, it is clear that it is of central importance that they should always be available in all tissues in adequate amounts. Recently, SAM and stable derivatives thereof have themselves been developed as drugs, particularly for nervous system and liver diseases (Bottiglieri, 1997, Lieber, 199).
As well as being converted to methionine, homocysteine can also be converted to cystathionine and then to cysteine in two successive reactions, both of which require vitamin B6 as a co-factor. Excessive accumulation of homocysteine can thus be partially dealt with by its metabolism along this pathway. However, this cannot occur if there is inadequate availability of vitamin B6. Vitamin B6 may, therefore, be of value in removing homocysteine, but not in generating SAM since it takes homocysteine out of the cycle.
There are four main forms of vitamin B12, cyanocobalamin, hydroxocobalamin, methylcobalamin and adenosylcobalamin. Methylcobalamin and adenosylcobalamin are unstable and very easily damaged by light. They are therefore unsuitable for use in dietary supplements or pharmaceuticals and are not necessary since they can be formed from cyanocobalamin or hydroxocobalamin within the body. The main form of vitamin B12 found in food is hydroxocobalamin (J Farquharson and J F Adams, British Journal of Nutrition 1976; 36:127-136). The main form used therapeutically and in nutritional supplements is cyanocobalamin, chosen because it is the most stable form and therefore easiest to synthesise and formulate. All oral nutritional and pharmaceutical preparations of vitamin B12 which are commonly available use cyanocobalamin.
In normal individuals vitamin B12 is absorbed from the gastro-intestinal tract with the aid of a specific binding protein, known as intrinsic factor (IF) which is produced by the stomach. The normal daily requirement for vitamin B12 is in the region of 0.1 to 2.0 microg/day according to various expert committees. There is normally an extensive enterohepatic recovery of vitamin B12. This recovery is impaired if IF is lacking, if the distal ileum is damaged, e.g. by radiation or disease, or has been removed by surgery. The daily loss of vitamin B12 can be then considerably increased, at the same time as the food-bound vitamin B12 cannot be absorbed. A lack of IF thus produces a deficit of vitamin B12 within the body even though there are apparently adequate amounts in the food. The deficiency, known as pernicious anaemia, is treated by injections of vitamin B12 as cyanocobalamin or hydroxocobalamin as it is generally believed that oral administration of vitamin B12 will be ineffective.
However, it is not well known that it is possible to treat vitamin B12 deficiency by oral administration of mg-doses even in the absence of IF, or when absorption is disturbed by other causes. This is because there is also a passive diffusion of the vitamin through the intestinal wall into the body without any need for IF. The passive absorption is dose-dependent and amounts to about 1-2% of doses of 1 mg or more. Two studies using cyanocobalamin have shown that oral doses of 1-2 mg/day are fully adequate to provide vitamin B12 even in patients with pernicious anaemia (H Berlin et al, Acta Medica Scandinavica 1968; 184:247-258: A M Kuzminski et al, Blood 1998; 92:1191-8). Long-term oral treatment with 1 mg cyanocarbalamin per day has been calculated to restore the body stores of vitamin B12 to the same extent as 1 mg hydroxocobalamin given by injection each third month (Berlin R et al, Acta Medica Scan. 1978; 204:81-4). However it is not well known by doctors that a vitamin B12 deficiency can be treated orally: in a survey of 245 internal medicine specialists in Minnesota none had used oral vitamin B12 to treated pernicious anaemia and only 1% had used oral vitamin B12 to treat a dietary deficiency: injection of cyanocobalamin was the treatment used by those doctors (F A Lederle, JAMA 1991; 265:94-95).
Recent studies have demonstrated that vitamin B12 deficiency states are much commoner in the general population, especially in the older population, in smokers, and in those at risk of cardiovascular disease than had previously been thought. One marker of this is an elevated level of homocysteine in plasma. For example, 44 apparently healthy men had elevated levels of homocysteine coupled with highly significantly subnormal blood levels of vitamin B12 (J B Ubbink et al, American Journal of Clinical Nutrition 1993; 57:47-53). A high proportion of older outpatients attending a clinic had deficiencies of vitamin B12 (L C Pennypacker et al, Journal of the American Geriatric Society 1992; 40:1197-1204). In a Massachusetts population 40.5% of older individuals and 17.9% of younger people were found to have low or low normal serum vitamin B12 (J Lindenbaum et al, American Journal of Clinical Nutrition 1994; 60:2-11). In Europe 63% of healthy elderly people were found to have an elevated level of homocysteine or methylmalonic acid, or other markers of vitamin B12 deficiency (E Joosten et al, American Journal of Clinical Nutrition 1993; 58:468-76). In healthy older Dutch people, 23.8% were found to be vitamin B12 deficient (DZB van Asselt el al, American Journal of Clinical Nutrition 1998; 68:328-334). In many of the individuals reported in these studies there were also deficiencies of folate and sometimes of vitamin B6 which exaggerated the problems associated with vitamin B12 deficiency.
Most of the people with these deficiencies apparently have adequate vitamin B12 levels in the diet. Their problems must therefore relate to inadequate levels of IF or to some other metabolic problem. If there are deficits of IF, standard medical treatment is to give injections of vitamin as hydroxocobalamin or cyanocobalamin and not oral treatment. However, to give regular injections to the very large numbers of apparently healthy people affected by vitamin B12 deficiency is clearly not a practical proposition. Oral vitamin B12 is usually given only when there is a dietary deficiency. Then the form of the vitamin which is given is always cyanocobalamin: no oral preparations of hydroxocobalamin are available.
Surprisingly, we have noted that cyanocobalamin may be less than optimum and may even be toxic in individuals with vitamin B12 deficiency. One reason is that there appear to be adverse interactions between vitamin B12 deficiency and the presence of cyanide. Cyanide is relatively common at low levels in the environment, being present in smoke, particularly tobacco smoke, and in certain foods. It may also be generated in small amounts in the course of normal metabolism since the body contains effective mechanism for cyanide detoxification. There is evidence that the consequences of vitamin B12 deficiency for the nervous system are much more serious in the presence of situations where cyanide may be generated or not detoxified (A G Freeman, Journal of the Royal Society of Medicine 1988; 81:103-106: A G Freeman, Journal of the Royal Society of Medicine 1992; 85:686-7). Whereas cyanocobalamin will not alleviate any cyanide excess and may even make the situation worse because of its cyanide content, hydroxocobalamin not only corrects a vitamin B12 deficiency but actually acts as an antidote to cyanide poisoning by binding cyanide (J C Forsyth et al, Clinical Toxicology 1993; 31:277-294). On the basis of these observations, therefore, Freeman has argued that cyanocobalamin should actually be withdrawn and replaced by hydroxocobalamin. However, Freeman has also argued that only hydroxocobalamin given by injection should be used, stating xe2x80x9cI strong oppose any treatment for pernicious anaemia other than parenteral hydroxocobalaminxe2x80x9d (A G Freeman 1999; Lancet 353:410-411).
General Description of the Invention
In view of the widespread occurrence of vitamin B12 deficiency states in the general population, in view of the fact that most of these deficiency states are not due to lack of vitamin B12 in food, and in view of the potential toxicity or lack of efficacy of high doses of cyanocobalamin, we propose the formulation of high doses of hydroxocobalamin for oral administration. Furthermore in view of the very common co-occurrence of folate deficiency in these same populations and in view of the fact that folate and vitamin B12 are so closely linked metabolically we propose that the hydroxocobalamin should always be formulated with folic acid or a related compound with folate bioactivity such as methyltetrahydrofolate. Such formulations will be particularly valuable in generating SAM for methylation reactions.
In order to ensure adequate absorption of vitamin B12, even in the absence of intrinsic factor, we propose that the formulation should provide a minimum dose of 0.5 mg hydroxocobalamin per day, should sometimes include more than 5 mg/day and should provide a maximum dose of 50 mg per day, preferably within the range of 1 mg per day to 10 mg/day. The hydroxocobalamin should be formulated with folic acid or a related bioactive derivative also providing a minimum of 0.5 mg folate per day and a maximum of 50 mg/day.
There is an extensive literature relating to the uses of folic acid and of vitamin B12, particularly in relation to the lowering of homocysteine levels. There is less literature relating to their uses in situations where enhancement of methylation is important. Almost all of the literature deals with the use of folic acid combined with cyanocobalamin as the source of the vitamin B12. Occasional authors mention hydroxocobalamin in passing as a possible alternative source, but none emphasises or even discusses the advantages of using hydroxocobalamin in view of the potential toxicity of cyanocobalamin.
Three citations are of particular importance in the context of the combined use of high or relatively high doses of vitamin B12 and folic acid. A patent EP-A-0558960 in the name of Wxc3x6rwag discloses primarily the use of thiamin, in association with other nutrients, in medicaments for patients whose are abusing alcohol. This specification describes folic acid and vitamin B12 as additional ingredients to thiamine in such a medicament. Any form of vitamin B12 is described as being acceptable in the formulation, with no discussion of the possible toxicity of cyanocobalamin or of the advantages of hydroxocobalamin. Thiamine is always an essential component and the specification does not disclose the value of formulation of hydroxocobalamin and folic acid.
EP-A-0595005 Vesta discloses the combination of three nutrients, folic acid, vitamin B12 and vitamin B6, specifically for the treatment of elevated homocysteine levels. Vitamin B6 is absolutely required in this formulation. The source of vitamin B12 is stated as being cyanocobalamin or hydroxocobalamin. There is no suggestion that hydroxocobalamin is the preferred form, or that cyanocobalamin may potentially be toxic. All of the examples of oral products specifically refer to cyanocobalamin and not to hydroxocobalamin.
A paper by M den Heijer et al (Arterioscler Thromb Vasc Biol 1998; 18; 356-61) discusses the administration of a formulation for lowering homocysteine levels comprising 0.4 mg of hydroxocobalamin, either alone or with 0.5 mg/day or 5 mg/day of folic acid. The authors found that hydroxocobalamin contributed little to the lowering of homocysteine levels with the main effect being due to folic acid. The dose of hydroxocobalamin in this citation is lower than provided for in the present specification and is probably too low to be consistently beneficial in individuals who have any problems in the absorption or metabolism of vitamin B12.
Thus, none of the prior art describes the specific importance of higher oral doses of hydroxocobalamin of 0.5 mg/day or above when combined with folic acid. None of the prior art discusses the specific uses of hydroxocobalamin and folic acid to promote the synthesis of SAM for methylation reactions.
As discussed above, there is increasing interest in using SAM, or derivatives of SAM, as therapeutic agents themselves for the promotion of methylation reactions. Once SAM has donated its methyl group, the molecule left is S-adenosyl-homocysteine, which is rapidly converted to homocysteine. Thus, administration of SAM has the potential to increase the formation of homocysteine substantially, particularly in patients with deficits of folic acid of vitamin B12 who may not be able to metabolise the homocysteine normally. It will therefore be particularly appropriate to include hydroxocobalamin and folic acid in formulations of SAM or derivatives of SAM for any therapeutic purpose for which the SAM is being administered.
Other ingredients may optionally be added to the basic hydroxocobalamin/folate formulation. These may include any other essential nutrients and any drugs. Such formulations will be particularly appropriate when treatment is given to a population which seems to be at particular risk of, or particularly affected by single or combined deficiencies of vitamin B12 or folate. Such patients include all elderly patients being treated for any disease, all patients of any age being treated for psychiatric or neurological diseases, including patients with depression, bipolar disorder, schizophrenia, multiple sclerosis, dementias, including Alzheimer""s disease, panic attacks, anxiety, social phobia, and Parkinson""s disease, all patients with fatigue of any origin, and all patients with or at risk of cardiovascular disease, liver diseases, gastrointestinal, reproductive or skin diseases, or any other diseases. These populations for various reasons are often at risk of nutritional deficiencies and deficiencies of vitamin B12 or folic acid may often limit the desired therapeutic responses to drug treatment of any of the above illnesses. It is therefore within the scope of the invention to add hydroxocobalamin and folic acid to any oral formulation of any drug for the treatment of the above diseases.